In the field of commercial vehicles, the reduction in engine speed in order to bring the engine and transmission speeds into line with one another when shifting up a gear is typically facilitated by means of existing engine-brake flaps. Depending on the location of the flap (upstream or downstream of an exhaust turbocharger) it can take a relatively long time to reduce the engine speed, since the exhaust gas has to be built up upstream of the flap as far as the combustion chamber. The piston must expel the exhaust gas in the cylinder in opposition to the accumulated exhaust gas in the exhaust tract. Additional work is involved. As a result, the engine speed is reduced.
Besides the length of time involved in reducing the engine speed by means of the engine-brake flap, the known method has the further disadvantage that a turbocharger lag can occur at the end of the upshifting process. The reason for this is that the flow through the exhaust-gas turbine of the exhaust turbocharger is reduced due to the build-up of exhaust gas and the boost pressure therefore falls considerably in the engine-braking mode.